Light-dispersive probe

ABSTRACT

A surgical probe is disclosed that disperses light sideways from its fore end. A light-dispersive and light-transmissive medium is enclosed within a housing. The medium is preferably divided into sections containing different concentrations of a light-dispersing material within a matrix. The sections are preferably separated by non-dispersive spacers. At the tip end of the probe is preferably a mirror to reflect the light back into the dispersive medium. The mirror may consist of layers with multiple indexes of refraction. By these features, especially in combination, the directionality and intensity distribution of the emitted light may be controlled. The present invention is designed to be useful especially in the use of laser energy in the percutaneous, interstitial irradiation of tissue growths.

FIELD OF THE INVENTION

[0001] The present invention relates to a surgical probe that operatesin conjunction with a source of light and a conduit by which the lightis conveyed from the source of light to the probe. The invention relatesparticularly to a light-emitting probe that disperses light over asubstantial length of the tip of the probe.

BACKGROUND OF THE INVENTION

[0002] Surgeons have for many years used laser energy as a preferredmeans of light energy to achieve a variety of surgical effects. Amongother effects, such energy can cut, vaporize, ablate or coagulatetissue. Based on various parameters, it is possible to irradiatediseased tissue, and cause its coagulation and necrosis, withoutinjuring in a significant degree adjacent tissue that is healthy. It isknown in hyperthermia, for example, that carcinogenic tissue, beingweaker than healthy tissue, will necrose when exposed to temperaturesfrom ca. 42 to 45 degrees Celsius, whereas healthy tissue, in general,will begin to necrose when heated to ca. 60 degrees Celsius.

[0003] When used interstitially, a probe is inserted into the tissue tobe treated. In some interstitial cases, the surgeon desires to irradiatea generally spheroidal pattern about the fore end of the probe, anddesires that the irradiation should be of dispersed, uniform intensityand thus progressively yield a controlled zone of necrotic destruction.The emission of light at the fore end of the probe is therefore bothradial, or sideward, and axial, or forward. In other cases, as forexample in order to achieve a cylindrical or ellipsoidal pattern oftissue destruction about the probe, only radial or sideward emission isdesirable, and axial or forward emission is not. Typically, it ispreferred that the radial emission should be dispersed over apredetermined surface area of the probe and at a generally uniformintensity. More and more, such probes are used percutaneously, and it isthen desirable to use a tracking means to determine their location. Itis then desirable to make the probe conspicuously visible using such atracking device.

[0004] When operating intraluminally, as for example in atheroscleroticvessels, a surgeon may desire irradiation patterns similar to those ininterstitial use. In some cases, the surgeon may even use a probe thatcan, to a limited degree, irradiate tissue that lies aft of the probe.

[0005] Generally, laser light that is conducted from a source of laserenergy through a fiberoptic cable will not be emitted when it encountersthe boundary of the light-conductive core of the fiber-optic material.The boundary is a smooth interface between the core of the fiber and acladding about the core. The indexes of refraction of the cladding andcore are selected such that the light is kept inside the core by totalinternal reflection until it is conducted to the distal end of thefiber-optic. Moreover, the light that may be emitted from the distal endof the fiber-optic cable will typically manifest a Gaussian intensitydistribution: a preponderance of the emitted light is directed parallel,or nearly parallel, to the direction of the longitudinal axis of thefiber-optic cable.

[0006] Surgical probes that control dispersive radial and axial emissionfind use in photodynamic therapy, especially at low powers on the orderof milliwatts. Probes similar to but more durable than the ones used inphotodynamic therapy (PDT) find use in hyperthermia, in which powers ofan order of magnitude of watts are usual, and a power of 30 watts is notunusual. It is also possible to enhance the effect of photodynamictherapy by concurrent use of hyperthermia. A probe suitable forhyperthermic treatment, however, must be able to withstand thetemperatures that are produced for the therapy.

[0007] In order to produce a useful output for these and other purposes,it is necessary to alter the direction of the laser light from an axialto a radial direction and to ensure that the intensity of the emittedbeam is smooth and uniform, with an absence of “hot spots”.

[0008] U.S. Pat. No. 4,592,353 to Daikuzono discloses a laser probe thatcan be used in direct, interstitial contact with tissue. The laserenergy is coupled into the probe, which has no cladding. A coolant isapplied to the junction, or gap, between the probe and the fiber-opticcable. Such probes have been used for interstitial coagulation andnecrosis of tumors. Such procedures draw on principles of hyperthermiafor tumor destruction. This probe, however, emits light from the end ofthe probe, using a lens to disperse the light in a cone with a wholeangle of no more than 45E.

[0009] U.S. Pat. No. 5,380,318, also to Daikuzono, discloses a contactprobe that disperses the emitted light in directions other than forwardalong the longitudinal axis of the fiber-optic. In one embodiment theprobe is conical, and the external surface of the probe is roughened oris coated with irregularly-shaped transparent particles that willscatter the light. In another embodiment, the probe is a hollow tube orcap, and the inner surface of the cap is roughened or frosted. Whilethese probes are more effective than the probes in Daikuzono '353 indiverting the laser energy from an axial direction to a radial one, theystill emit a substantial proportion of the laser energy axially forwardfrom the tip of the probe. These devices also show a significant peak inradiation intensity level with the tip of the probe.

[0010] U.S. Pat. No. 5,520,681 to Fuller et al. discloses a probe thatdisperses light by means of porosity or other inclusions within theprobe. While these probes disperse the laser energy, they also generateheat, which may be harnessed for therapeutic use. Absorbent inclusionsmay be used to increase heating.

[0011] U.S. Pat. No. 5,054,867 to Wagnieres et al. discloses anapparatus for irradiating the bronchi of a patient for use inphotodynamic therapy. A fiber-optic is surrounded by a first tube ofpolytetrafluoroethylene (PTFE); a brass cylinder holds the fiber-opticand tube in fixed axial position. Silicone, interspersed with titaniumdioxide, fills the tube, but for a small air gap next to the brasscylinder. At the distal end of the first tube is set an aluminumcylinder, the proximal face of which acts as a mirror to light that isincident upon it. The aluminum cylinder is held in place by means of asecond tube of PTFE which surrounds the first tube, leaving a smallannular air gap between itself and the first tube, and extending beyondthe end of the first tube. A PTFE plug is inserted at the distal end ofthe second tube, thus helping to hold the aluminum cylinder in place.The titanium dioxide is interspersed more heavily at the ends of thesilicone-filled tube, near to the distal end of the fiber-optic and tothe mirror face of the aluminum cylinder, causing the central region ofthe inner tube to emit less of the laser radiation than its distal andproximal regions. A trough-shaped reflective coating may be provided onthe inside of the outer tube, to produce irradiation over only part ofthe circumference of the probe. This probe, having a metal reflector,will be limited in the powers that can be applied, for at high powers,the aluminum mirror face will absorb laser energy and may lead todestructive overheating.

[0012] U.S. Pat. No. 5,908,415 to Sinofsky discloses a transparent,plastic tube which surrounds and extends beyond the distal end of afiber-optic cable. A silicone matrix, with light-scattering particlesuniformly distributed therein, fills the tube. At the distal end of thetube is a reflective surface, and a plug caps the tube off. The lighttraveling from the fiberoptic cable to the distal end of the tube iscomplemented by the light that is reflected back from the reflectivesurface, to produce a comparatively uniform light intensity along thelength of the tube. The distance between the distal end of the fiberoptic and the reflective surface, and the concentration of thescattering particles, are selected to create an intensity distributionpattern that does not vary more than plus or minus 20% along the lengthof the tube. No air bubbles should be within the matrix. While on theone hand this fiber-optic device produces a relatively uniform radialemission and while it is relatively easy to manufacture inasmuch as ithas a uniform concentration of scattering particles, on the other handthe probe depends overmuch on the back reflection from the distal end ofthe device in order to achieve uniformity. The load that is put on themetal reflector can lead to overheating.

[0013] U.S. Pat. No. 5,431,647 to Purcell et al. describes a fiber-opticcable the core of which is stripped of its cladding over a distallength. Over that stripped length is snugly fitted a transparent sleevein which light-scattering particles have been embedded. The sleeve actsas an extension of the core, so that light enters the sleeve and isscattered out sideways. Abutting the distal end of the fiber-optic is ametallic mirror to reflect back the light that has not been scatteredand emitted through the sleeve. The mirror is held in place by atransparent cylindrical cap which also surrounds the sleeve and whichaffixes to an outer buffer of the fiber-optic cable. An air gap ismaintained between the cap and the sleeve, and acts like a cladding tothe fiber and sleeve. Intensity distributions varying no more than plusor minus 30% are reported to be easily obtained. In this probe, however,little is done to randomize the laser energy before it reaches thedistal metallic mirror, and for this reason, if high powers are used,the mirror will overheat.

[0014] U.S. Pat. No. 5,269,777 to Doiron et al. describes a fiber-opticfrom which the jacket has been stripped at the distal end. Abutting andextending fore of the fiber-optic is a first silicone portion.Surrounding the first silicone portion is a silicone sleeve, in whichare embedded light scattering particles. The concentration of theparticles may be varied to achieve uniform or otherwise specified outputpatterns. Within the first silicone portion can be distributed lightscattering particles, whether in discrete blocks or in continuouslygraded or melded concentrations. A sheath surrounds the silicone sleeveand a portion of the jacket that has not been stripped from thefiber-optic cable to provide the necessary rigidity to the tip assembly.It is asserted that the output pattern is substantially independent ofthe divergence of the laser beam that is coupled into the fiber-optic.This probe has little in its design to prevent the forward emission ofthe laser energy. In practice, either it will be limited to low powersor to applications where forward emission is immaterial or desired, orelse the forward emission will be reduced by a concentration ofdispersant that causes a non-uniform radial emission pattern.

[0015] U.S. Pat. No. 4,660,925 to McCaughan describes a fiber-opticcable that has been stripped of its buffer and cladding at the fore end.The distal end of the fiber-optic is carefully cleaved and polished.Layers of a scattering medium are applied to the exposed portion of thefiber-optic. Each layer is inspected and polished manually to ensure aspherically uniform emission of light, with concentrations of scatterersincreasing logarithmically to the fore end, thus ensuring a uniformcylindrical distribution. A tube is tightly fitted over the paintedportion of the fiber-optic. No air or contaminants must enter betweenthe tube and painted portion. Little is done in this probe to randomizethe laser energy traversing the fiber-optic, and the titration of thescattering medium according to a logarithmic pattern is not easilyachieved. As a result, this probe will not find application at highpowers.

[0016] U.S. Pat. No. 5,947,959 to Sinofsky discloses a device in which atransparent tube is affixed to the distal end of a fiber-optic cable.The tube surrounds and extends beyond the optical fiber. The tubecomprises a single chamber which is filled with a diffusive medium whichincorporates light-scattering particles of a uniform concentration andwhich is characterized by a single dielectric constant. A metal plug,typically gold, is set at the distal end of the tube, and servesprimarily to allow image-guided location of the distal end of the tube.Light that reaches the metal plug can cause it to heat, and such heatmay damage the tube or surrounding tissue. A dielectric reflectorconsisting of a stack of layers of different, alternating dielectricconstants formed on a glass substrate and is placed aft of the metalplug. The dielectric constant of the first layer is preferably greaterthan the dielectric constant of the diffusive medium. The interfacesbetween the layers reflect a high proportion of the light backward intothe tube, while generating minimal heat at the interfaces. Theinterfaces are spaced to produce constructive interference of thebackward reflected light, assuming that the light is traveling axially.Where the dielectric reflector is used with a metal reflector, the metalensures that forward emission out of the distal end of the tube is nilto negligible, though some of the light will be absorbed by thereflector and be converted to heat. Where the dielectric reflector isused without a metal reflector, it is assumed that the amount of lightthat is emitted forward is insignificant and will not injure tissue ordamage other instruments. However, the laser energy reaching thedielectric reflector will have been at least partly scattered andtherefore there will be a wide range of incidence angles at theinterfaces. Light incident at wide angles will not benefit fromconstructive interference, so the dielectric reflector will undesirablypermit the wider-angled energy to propagate through.

[0017] Each of the above devices found in the prior art seeks to divertsome or all of a laser beam from an axial direction and emission to aradial direction and emission. However, none is practical in dealingwith powers that could lead to forward emission that could undesirablyinjure tissue fore of the device or with powers that could undesirablyoverheat a reflector at the distal end and thus destroy the device.

[0018] What is needed is a device which effectively randomizes the pathof the laser energy as it is propagated through the radially emissiveportion of the device and achieves substantially uniform radial emission(or other controlled emission patterns), but which even at high powersgenerates immaterial heat at the device and can control the level offorward emission to a therapeutically exiguous amount.

SUMMARY OF THE INVENTION

[0019] The invention comprises a probe that is affixed to the fore endof a fiber-optic cable. The probe comprises a tube, or protectiveoptical cap, that attaches to the distal end of the fiber-optic. Thefore portion of the fiber-optic is stripped of buffer.

[0020] In one aspect of the invention, the tube is divided intosections. Separating the sections are optical spacers or rods, whichfunction like bulkheads. Each section is filled with a dispersingmedium, preferably a transparent matrix into which a dispersing materialis placed. Each dispersing medium has distinct dispersive powers.

[0021] In another aspect of the invention, the tube is divided intosections, each filled with dispersing media having distinct dispersivepowers, and a reflector is provided at the distal end of the tube toreflect light back into the foremost section.

[0022] In a third aspect of the invention, the tube contains adispersing medium and is provided at its distal end with a reflectorcomprising layers of material each of which has multiple indexes ofrefraction.

[0023] Another aspect of the invention is a method of forming such aprobe, while preventing or eliminating, air bubbles in the dispersingmedium.

[0024] To achieve uniform radial emission with respect to the first twoaspects of the invention, the density of the dispersing material, ordispersant, ranges from least dense at the section abutting the distalend of the fiber-optic, to most dense at the section at the distal endof the tube. Other emission patterns may be achieved by, among otherthings, varying the concentrations of dispersant, or the composition ofthe dispersants and hence their respective reflective, refractive and/ordiffractive capacities, or by adjusting the matrix and hence thedifference between its index of refraction and that of the embeddeddispersant. The field of emission may be controlled by masking a surfaceof the probe with a reflective coating.

[0025] The bulkheads separating one section from the next are preferablyformed of a transparent medium that has an index of refraction greaterthan the indexes of refraction of the matrixes found in any of thesections, and thus assures an index mismatch and accordingly a partialreflection. The greater the mismatch, the greater will be the Fresnelreflection. The bulkheads may have a common index of refraction, or mayhave different compositions and therefore different indexes, accordingto the desired result. Furthermore, if a surface of a bulkhead is givena partially reflective coating, then the Fresnel reflection may befurther controlled and enhanced.

[0026] As the laser energy comes to each bulkhead, some of the energy isreflected back into the section through which it has just passed forfurther dispersion, and some portion is coupled into and refracted bythe bulkhead, and transmitted into the next section. Inasmuch as thepath of the laser energy will have been randomized, more will be subjectto Fresnel reflection at the interface with the bulkhead than if it hadnot been randomized. The portion which is back-reflected runs thedispersion gauntlet again and will be substantially emitted from thesection. The emission from the return path complements the emission fromthe forward path, helping to provide a more uniform output.

[0027] The distal end of the probe may be sealed off with a plug toprotect the contents of the tube from dilution or contamination. Toprevent or mitigate any unwanted forward transmission, a reflector isincluded aft of the plug. Optimally, a reflector is selected whichinterdicts the forward propagation of laser energy incident upon thereflector at wide angles.

[0028] Especially in hyperthermic procedures, the probe may besurrounded by a transparent sheath, and a fluid coolant may becirculated between the probe and the sheath, thus cooling both thetissue and the probe.

[0029] The Fresnel reflection at the bulkheads reduces the amount oflaser energy that reaches the distal reflector, and thus mitigatesheating at the distal end and/or forward emission. The Fresnelreflection further smoothes the gradient of radial emission that wouldotherwise result at the junction of sections of differing dispersivecapacities.

[0030] In certain applications, however, especially ones requiring lowpowers, use of a distal reflector that does not overheat and thateffectively reflects light having wide angles of incidence may obviatethe need for bulkheads and even varying the concentration of thedispersant. As the active length L of the probe increases, a singleconcentration of dispersant may not be sufficient to yield uniformradial emission. In such a case, it is possible to vary theconcentration of the dispersant. It is also possible to have discretesections of matrix (with no intervening spacers) where the matrixes havediffering indexes of refraction, and thus cause backward reflections andincrease the optical path. Conversely, in such low-power applications orapplications where emission of light forward from the probe isacceptable, the use of bulkheads may obviate the need for a distalreflector.

[0031] All the materials used in the probe should in general exhibitlittle absorption of light and therefore generate minimal to no unwantedheat. The principal exception to this constraint occurs in low-powerapplications. In such applications, the reflector may be a metallicreflector.

[0032] According to one aspect of the invention, a light-emitting probecomprises a flexible, light-transmissive housing having a proximal end,adapted to be mounted to and to receive light from a fiber-optic, and aclosed distal end; at least one optical spacer dividing the length ofthe interior of the housing into at least two sections such that themost proximal section abuts the fiber-optic; and a light-transmissiveand light-dispersing medium filling each section.

[0033] The housing and the light-dispersing medium are preferablylight-transmissive in the sense that they permit light to pass throughthem without significant absorption, and thus without the heating thatwould result from the absorbed energy. The light-transmissive housingmay be, but need not be, transparent in the sense that a clear imagecould be seen through it. Because the light passing through the housinghas already been dispersed by the light-dispersing medium, there isusually no need to avoid further dispersion as the light passes throughthe housing. The light-transmissive housing and the light-transmissiveand light-dispersing medium need to be transmissive only to light of thefrequency that is intended to be used with the particular probe. Thus,where the probe is intended to be used with infra-red light, the housingand the light-dispersing medium are not necessarily light-transmissivein visible light.

[0034] The probe may comprise a reflector at the distal end of the mostdistal said section. The reflector may comprise a metal layer. Thereflector may comprise a mirror of thin reflecting film layers.Individual ones of the thin layers may be reflecting, and the thinlayers may then be layers of silver film. Instead, the layers may bereflecting only in combination, for example, because of changes inrefractive index at the boundaries between adjacent layers.

[0035] The probe may further comprise a sheath surrounding said probeand arranged in use to be supplied with a coolant liquid. The probe maythen further comprise a catheter surrounding the optical fiber-optic anddefining channels to supply and remove said liquid coolant.

[0036] According to another aspect of the invention, a light-emittingprobe comprises: a flexible, light-transmissive housing, having aproximal end adapted to be connected to a source of laser light and adistal end. There is a light-transmissive and light-dispersing mediumwithin the housing, divided along the length of the housing into atleast two sections having distinct light-dispersing properties. Areflecting means at the distal end of the housing is arranged to reflectlight back into the light-transmissive and light-dispersing medium.

[0037] A further aspect of the invention provides a light-emitting probecomprising a flexible, transparent housing, having a proximal endadapted to be connected to a source of laser light and a distal end. Alight-transmissive and light-dispersing medium is within the housing. Areflector at the distal end of the housing is arranged to reflect thelight back into the light-dispersing medium. The reflector compriseslayers designed to reflect the light back into the housing and exhibitsmultiple indexes of refraction at each layer.

[0038] For any aspect of the invention, coolant may be delivered via acatheter to abstract adventitious heat. Coolant serves a furtherpurpose: a premature build-up of heat within the tissue adjacent to theprobe is prevented. Were the tissue to overheat to the point ofcharring, the char would obstruct the further desired penetration of thelaser energy and compound the overheating and lead to the possibledestruction of the probe.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] For the purpose of illustrating the invention, there are shown inthe drawings forms of the invention which are presently preferred; itbeing understood, however, that this invention is not limited to theprecise arrangements and instrumentalities shown.

[0040]FIG. 1 shows an axial sectional view of one form of probeembodying the invention. In the interests of clarity, the widthwisedimensions have been greatly enlarged in comparison with the lengthwisedimensions.

[0041]FIG. 2 shows a view similar to FIG. 1 of a second form of probeembodying the invention.

[0042]FIG. 3 shows a view similar to FIG. 1 of a third form of probeembodying the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0043] Referring to FIG. 1, one form of probe according to theinvention, indicated generally by the reference numeral 10, is attachedto the distal (foremost, or tip) end of an optical fiber 12 comprising acore 14 surrounded by a cladding 16. Surrounding the optical fiber is afiber buffer 20 made of a plastic known as TEFZEL® (a registeredtrademark of E. I. DuPont de Nemours, Wilmington, Del.). The front facesof the core 14 and the cladding 16 are cleaved flat. The buffer may becleaved flush with the front faces of the core and clad, or it may becleaved and removed aft of those front faces. If it is removed aft (asshown in FIG. 1), then it may be filled with matrix and dispersant fromthe first section 28 a, as described below. A tube 22 surrounds thefront end of the fiber buffer 20 and extends forwards of the distal endof the optical fiber 12. The tube 22 overlaps the fiber buffer 20 by adistance sufficient to give strength to the bond between the tube andthe fiber-optic cable, and is bonded to the fiber buffer by adhesive.

[0044] The space within the tube 22 forward of the end of the opticalfiber 12 is separated into three sections, 24 a, 24 b, and 24 c by twooptical spacers in the form of bulkheads 26 a and 26 b. Each section 24a, 24 b, and 24 c is filled with a light-transmissive andlight-dispersing medium 28 a, 28 b, and 28 c, respectively. Thedispersing medium consists essentially of a transparent matrix 30,symbolized in the drawings by the clear area in each section 24 a, 24 b,and 24 c, which in turn has interspersed within itself a dispersivematerial or dispersant 32 symbolized by the dots strewn within eachsection. An end plug 34 closes the tube 22 forward of the front (mostdistal) section 24 c. Reflecting means 36 lies between the end plug 34and the front section 24 c. The distance L from the cleaved end face ofthe core 14 to the proximal face of the reflecting means 36 is theactive length of the probe.

[0045] The fiber-optic cable, comprising the core 14, the cladding 16,and the fiber buffer 20, and including the extra width of the tube 22,is slim enough that it is still able to slip down a working channel of acatheter, cannula or endoscope, typically having outer diameters in therange of 7 French. In the preferred case, the outer diameter of the core12 is 600 microns, or 0.6 mm, and the outer diameter of the fiber buffer20 is 750 microns, or 0.75 mm. Smaller cores (e.g. 400 microns) are alsopreferred. A fiber-optic cable composed of silica is usually suitablefor transmitting the laser energy. The laser energy typically used willbe over a range of wavelengths that penetrate tissue and coagulate it.The wavelength of 1,064 nm of the Nd:YAG laser is such a wavelength, asare 940 nm and 980 nm generated by diode lasers, and silica istransparent at those wavelengths. However, the invention is notrestricted to the use of near-infrared laser light, but can also beapplied in the visible region of light spectrum, so long as thefrequency of light chosen is compatible with the materials of the probeand answers the therapeutic need.

[0046] The tube 22 is composed of polytetrafluoroethylene (PTFE),commonly known as TEFLON, which a registered trademark of E. I. DuPontde Nemours (Wilmington, Del.). PTFE is a suitable material for the tubeinasmuch as it is flexible, biocompatible and optically transparent andexhibits little absorption of light and attendant heating. The PTFE tube22 constitutes a light-transmissive housing for the probe 10. The tube22 extends beyond the distal end face of the core 14 by a length L,called the active length of the probe; in the case depicted the workinglength is 30 mm. The outer diameter of the tube 22 is 1.1 mm. The tube22 extends aft of the cleaved distal end face of the core 14 for alength of 15.75 mm (0.62 inches), in order to give strength to the bondbetween the tube and the fiber-optic cable 12. The tube 22 is attachedto the fiber-optic cable by means of an adhesive 38. One such adhesiveis Dymax 1128-M, an ultraviolet-curable medical-grade adhesive availablefrom Dymax Corp. (Torrington, Conn.).

[0047] Silicone epoxy has been found to be suitable for the transparentmatrix 30. One suitable material is Mastersil 151 Clear, a siliconeepoxy having an index of refraction of 1.43, which can be obtainedcommercially from Master Bond, Inc. (Hackensack, N. J.).

[0048] It is possible, though not usually necessary, to vary the choiceof matrix from section to section, just as it is also possible, thoughnot usually necessary, to vary the choice of dispersant from section tosection. The index of refraction of the matrix and the dispersant may bethe same, or different. The matrix and the dispersant, like all othermaterials of the probe, should usually have a nearly null imaginaryindex of refraction, and thus have little to no absorption leading toattendant heating. The principal exception is in low-power applications,as for example PDT, where a significant proportion of the laser energycan be absorbed without causing excessive heating. In such applications,a metallic mirror reflector may be used as reflecting means 36,discussed below.

[0049] It is important, however, that the dispersant 32 should lie inthe path of the laser energy before that energy reaches the distal end34, 36 of the probe. The dispersant 32 assures that the path of thelaser energy is randomized. If it is desired to achieve a uniform radialemission, the density of the dispersant 32 is least at the section 24 aabutting the optical fiber 12 and greatest at the distal end 36 of theactive length L of the probe. The capacity to disperse light, and hencethe transmissivity, of each section 24 a, 24 b, 24 c, will thus differfrom that of the other sections.

[0050] Particles of titanium dioxide, aluminum oxide or silicon dioxidehave been found to be suitable materials for the dispersant 32. Thedispersant depicted in FIG. 1 is titanium dioxide, available in the formof titanium-dioxide-filled silicone epoxy such as Mastersil 151 White,from Master Bond. The titanium dioxide particles are optimally in rutilecrystalline form and have an index of refraction of 2.73. Silicone has arefractive index of 1.43. In the preferred embodiment, laser energy at1,064 nm from an Nd:YAG laser is used to treat tumorous growths, butdiode wavelengths of 940 nm and 980 nm can also be used. Preferably, theparticles should be less than 1 micron in diameter. The ratio ofMastersil 151 Clear to Mastersil 151 White, by weight, in sections 24 a,24 b and 24 c is 3,000:1, 1,900:1 and 1,200:1, respectively, for a 30 mmactive length L. In Mastersil 151 White, there are 30 grams of titaniumdioxide for every 300 grams of silicone.

[0051] Separating the sections are the bulkheads 26 a and 26 b. Thebulkheads are disc-like wafers or rods, measuring 750 microns indiameter (and 490 microns in a smaller tube variation) and 1 to 1.5 mmin length. The discs 26 a, 26 b are highly polished on surfaces normalto the longitudinal axis. They are fitted snugly between the dispersingmedia 28 a, 28 b, 28 c filling the sections 24 a, 24 b, 24 c.

[0052] Air pockets should be strictly avoided, as they createdestructive heat. Two steps have been found especially helpful as amethod of avoiding air pockets. In the first preferred step, the matrix30 and dispersant 30 are mixed to be completely homogeneous, withoutstreaks or swirls. During mixing, the selection of matrix and dispersantis subjected to a gauge vacuum of 25 mm of mercury. The vacuum inducesair that may be latent within the selection to froth at the surface ofthe mixture. The vacuum is then broken quickly, and as a result, the airbubbles that were induced to the surface burst into the atmosphere. Thisprocess is repeated until there are no streaks or swirls in theadmixture and until there is no more frothing of air.

[0053] In the second preferred step, the tube 22 is mounted onto theoptical fiber 12, and the dispersing media 28 a, 28 b, 28 c and thebulkheads 26 a, 26 b are assembled into the tube in order from theproximal (optical fiber) end towards the distal end 34, 36. The siliconeepoxy matrix of the dispersing media 28 a, 28 b, 28 c is in an unset,thickly liquid state in which it fills the space within the tube 22. Theselection 28 a of matrix and dispersant that is to be inserted firstinto the tube 22 is inserted under positive pressure. This first batchis carefully inspected for trails of latent air within the zone of thetube 22 to which ultraviolet-curable adhesive 38 is applied.

[0054] Under magnification and with a sharp needle (e.g. Dritz beadingneedle size no. 10/13 or Schmetz Microtex sharp needle 130/705 H-M80/12), a puncture is made at the most proximal point of the mostprominent air trail; in some cases, two punctures may be needed. Thepuncture is made in the part of the tube 22 where the dispersing medium28 a surrounds the stripped part of the optical fiber 12, behind the endface of the core 14. Thus, if the puncture creates an opticallysignificant blemish in the finished probe, it is in a region where nosignificant dispersion of light is occurring, and does not affect theperformance of the probe. As the end plug 34 is finally inserted intothe tube 22, it acts as a piston and purges latent air out of thepunctures. Matrix and dispersant will follow the air that is expressedthrough a puncture, and will seal such puncture as it hardens. Careshould be taken not to puncture the fiber buffer 20 surrounding opticalfiber 12.

[0055] Cubic zirconium has been found to be a preferred material for thebulkheads 26 a, 26 b. Its index of refraction is 2.12, which is suitablyhigher than the 1.43 of the silicone epoxy medium. It is opticallyisotropic, so that there are no constraints on orientation of axes dueto polarization, and it sustains little loss to absorption and othercauses. Cubic zirconium is available from Imetra, Inc. (Elmsford, N.Y.).Aluminum oxide (sapphire) can also be used as a suitable bulkhead.

[0056] It is desirable that the index of refraction of each bulkhead 26a, 26 b be greater than the greatest index of refraction found in anysection 24 a, 24 b, 24 c. Subject to that, the bulkheads may share acommon material and therefore a common index of refraction, or they mayhave differing composition, and thus differing indexes of refraction.The bulkheads exhibit low absorption and high internal transmissivity.The index of refraction of the tube 22 is to be less than any of theindexes of refraction of the sections. PTFE is the preferred materialfor the tube, and its index of refraction is 1.31. A lesser index ofrefraction promotes further internal reflection, which is necessary toextend the radial emission over a greater active length L of the probe.

[0057] Laser energy propagates through probe 10 as follows. The light isemitted from the distal face of the optical fiber core 14. Depending ona number of factors, including the length of the fiber-optic cable, itwill typically have a full-angle divergence of up to approximately 46degrees where the numerical aperture of the fiber is 0.39 andapproximately 57 degrees where the numerical aperture of the fiber is0.48. The bulk of the laser beam, however, will diverge from thelongitudinal axis of the core 14 only by several degrees, and thus theangular distribution of the beam will assume a Gaussian pattern. Theindex of refraction of the core 14 is that of silica, or 1.45; the indexof refraction of the medium 28 a in the section 24 a is two-fold: anindex of 1.43 for the silicone 30, and an index of 2.73 for the titaniumdioxide 32. The laser beam, as it is coupled into and through thesection 24 a, is immediately dispersed and randomized.

[0058] A portion of the randomized light hits the wall of the tube 22,and if the angle of incidence of the light (measured from the normal tothe incident surface) is less than the critical angle between the medium28 a and the tube 22, the light couples into and through the tube. Theamount of light energy remaining within the tube 22 is greatest at theproximal region of section 24 a, and tapers off to the least amount atthe distal region of the section. The amount of light that is emittedout of tube 22 also tapers off from the proximal region of the sectionto the distal region of the section, in dependence on the amount oflight in the tube and the scattering of that light.

[0059] The laser energy that propagates through section 24 a and reachesthe proximal face of bulkhead 26 a is subject to Fresnel's law. Havingbeen randomized, more of the light is subject to Fresnel reflection thanif it had not been randomized. Other things being equal, the greater thedifference between the indexes of refraction of section 24 a andbulkhead 26 a, the greater is the proportion of the light that isreflected. In the probe shown in FIG. 1, the difference in refractiveindex is approximately 0.69 (i.e., 2.12 1.43). The measured Fresnelreflection is on the order of 4% at each face or boundary interface ofthe bulkhead. The light reflected back into section 24 a will be emittedsimilarly to the light propagating forward as described above, and theamount of emitted light will taper in the reverse direction, with theamount being greatest near the bulkhead 26 a and least near the end faceof the optical fiber. The reversely tapering emission will complementand superimpose on the forward tapering pattern of the unreflectedlight. For practical purposes, the reflected light becomes trapped inthe section 24 a until it is emitted from that section.

[0060] As the light couples from the first bulkhead 26 a into the nextsection 24 b, the amount emitted typically rises at the interface, andthen tapers off towards the interface with the second bulkhead 26 b. Theinitial rise would be all the more pronounced, were it not for theback-filling performed by the Fresnel reflection from bulkhead 26 a backinto the first section 24 a.

[0061] Given that the proximal and distal faces of the bulkhead 26 a areparallel, the light will couple out and continue in the same directionin which it was coupled into the bulkhead. However, if the faces of thebulkhead are not parallel to each other and/or are not normal to thelongitudinal axis of the fiber-optic, the light propagating from thedistal face of bulkhead 26 a will take a different path.

[0062] As the light traverses through succeeding sections and bulkheads,similar effects are achieved to those described above for the firstsection 24 a and the first bulkhead 26 a. Thus, in each section, thereis an emission of forward-propagating light, which is greatest at theproximal end of the section, and an emission of reflected light, whichis greatest at the distal end of the section and which is superimposedon the emission from the forward-propagating light. The absolute amountof light in the tube decreases from each section to the next. Thedensity of the dispersant 32 can be increased in each successivesection, so as to increase the proportion of light scattered out of thetube. It is possible by this means to keep the absolute amount of lightemitted from different parts of the tube uniform, if that is desired.Other light distributions can be achieved by a suitable selection of theamount of dispersant 32 in each tube section 24.

[0063] In any embodiment of the bulkheads, one may apply a partiallyreflective coating to either the proximal or the distal face of any ofthe bulkheads, or to both faces, in order to enhance the back reflectionof the light. Such coatings are available commercially from numeroussuppliers. One such supplier is Spectrum Thin Films (Bohemia, N.Y.).

[0064] When the light propagates through the most distal section 24 c, aportion of it will reach the reflecting means 36 formed on the plug 34.For any light that has not been coupled out of the tube 22 by the timeit reaches the distalmost part of the foremost section, the reflectingmeans 36 stands ready to return the light to the prior section. Thesubstantial majority of the light incident on the reflecting means 36 isreflected back into the last section 24 c. The reflector 36 thusprevents the waste of energy that can be rendered therapeutic. Togetherwith the end cap 34, it also protects surrounding tissue from needlessinjury and adjacent instruments from needless damage that might becaused by the laser light beam escaping through the tip of the probe 10.

[0065] The reflected light returns along the same path by which it cameforward along the probe 10, and undergoes the same dispersion by thesections and partial reflection by the bulkheads as the forward pathunderwent. The light emitted after reflection by the reflecting means 36further complements that emitted on the forward path. The uniformity inthe emission of light from the tube 22 along the length of each sectionis dependent to a large extent on the balance between the amounts oflight entering that section from the proximal and distal ends. Thepartial reflection at the bulkheads 26 a, 26 b, thus reduces the amountof light that must reach and be reflected by the reflector 36 tomaintain any desired degree of uniformity in the emission of light fromthe active length L of the tube. The reduction in the amount of lightreaching the reflector 36 in turn reduces the absolute amount of lightabsorbed by the reflector, and thus reduces heating of the end plug 34by the absorbed light.

[0066] The plug 34 is a mushroom-shaped cap. It can be made ofoptical-grade, biocompatible materials, as for example. HP2R Lexan,obtainable from GE Plastics (Pittsfield, Mass.). Its dimensions areconformed to fit the tube 22 in which it is installed. It is affixed tothe distal end of tube 22 by an adhesive.

[0067] The plug 34 serves two purposes. First, it protects the interiorof tube 22 and the enclosed sections 24 from invasion by influents.Second, it provides a base on which the reflecting means 36 can beapplied.

[0068] The reflecting means 36 is preferably a reflective coating which,as generally understood, will reflect backward a substantial majority oflight impinging on it and will not absorb that light or otherwisegenerate unwanted heat. As shown in FIG. 1, the reflective coating 36comprises a mirror of thin layers of reflective film. Individual layersmay be reflective, or the layers may be reflective in the aggregate, forexample, dielectric layers with alternating dielectric constants. It isnot critical that the light reflecting backward from the differentlayers should benefit from constructive interference. As noted abovewith reference to the Sinofsky 959 reference, a constructiveinterference reflector consisting of a stack of quarter-wave-thicknesslayers may provide very good reflection of light rays traveling parallelto the axis, but may not efficiently reflect scattered light. Inpractice, it is feasible to use a reflector of layers having thicknessesapproximately equal to a quarter of the average of the wavelengths thatmay be propagated through the probe. Such a range may be from 940 nm to1,064 nm, as this range of wavelengths exhibits generally goodpenetration of tissue. Reflection coatings are available at numerousfacilities. One such facility is Spectrum Thin Films.

[0069] In a preferred embodiment, the reflector 36 consists of aplurality of layers of birefringent or other material that exhibitsmultiple indexes of refraction within the layers. The reflector can thusbe better able to control and redirect light of widely varying angles ofincidence. Such reflectors are described in U.S. Pat. No. 6,101,032 toWortman et al. Reflectors exhibiting such properties are available from3M Corporation (Minneapolis, Minn.) and can be applied to a substratesuch as glass or plastic (e.g. polyester) and in-set between theforemost section 24 c and the end plug 34.

[0070] If some portion of the light should emerge from the reflectingmeans 36 and out of the plug 34, it must be of an intensity anddirection that does not injure the tissue it impinges on or damage anyattendant instruments. In one empirical test, the forward transmissionfrom three dispersive probes was measured. The probes had no distalreflecting means and were substantially the same, except in the numberof spacers. The first probe had two spacers (distal and proximal),positioned to divide the probe into three nearly equal sections, viz.proximal, medial and distal. The forward transmission was 26.5%,relative to the energy introduced into the proximal end of the probe.The second probe (with one spacer) was like the first, except that wherethe first probe had a proximal spacer, the second probe had no spacerdividing the medial and proximal sections. The forward transmission ofthis probe was 38.3%, relative to the energy introduced into theproximal end of the probe. Finally, the third probe had no spacersdividing the proximal, medial and distal sections. Its forwardtransmission was 46.3%. The bulkheads manifestly reduce the amount offorward transmission of the dispersive probe.

[0071] In applications where low powers are used, as in PDTapplications, a metallic mirror reflector may be used as the reflectingmeans 36. Gold is a preferred metal, because of its low chemicalreactivity. It can be applied in various ways to the proximal surface ofthe plug 34 (e.g. by vapor or ion beam deposition), or a thin disc ofgold can be set between the plug 34 and the foremost section 24 c.Silver can also be used but it should be given an overcoat, as forexample of silica, to prevent its oxidation. In fact, if an overcoat ofthin reflecting film layers is applied, the silver not only is protectedfrom oxidation, but also is able to operate at higher powers than goldalone. If desired, a cooling sheath from a catheter, as described belowwith reference to FIG. 3, can to be used to abstract heat generated bythe metallic surfaces.

[0072] Each bulkhead 26 thus serves several functions. First, eachbulkhead acts as a checkpoint of the propagating laser beam. Someportion of the beam is reflected back at each bulkhead 26, thus reducingthe amount of light reaching the reflecting means 36. As such, thepotential for forward emission is reduced. Second, each bulkheadsmoothes the gradient of emission between two sections. Third, eachbulkhead separates the contents 28 of adjacent sections 26 and thusprevents intermingling and preserves the different concentrations of thedispersant 32 in the different sections.

[0073] In applications requiring low powers, the use of a distalreflecting means 36 that is effective in reflecting light having wideangles of incidence may obviate the need for bulkheads 26. On the otherhand, in such low-power applications or in applications where limitedforward emission of light is acceptable, then the use of bulkheads 26may obviate the need for a distal reflecting means 36.

[0074] Referring to FIG. 2, the second embodiment of the invention isgenerally similar to the first embodiment shown in FIG. 1, and featuresembodied in FIG. 2 that are common with features in FIG. 1 share likenumbers, increased by 100. Thus, a probe 110 in FIG. 2 is attached to anoptical fiber 112 having a core 114 surrounded by cladding 116, encasedwithin a buffer 120. A tube 122, an end cap 134, a reflector 136, and soon, may be substantially the same as those described above withreference to FIG. 1. However, the probe 110 shown in FIG. 2 has only onebulkhead 126 a and only two light-dispersing sections, 124 a and 124 b.

[0075] As shown in FIG. 2, a portion of the external surface of thefirst section 124 a within the working length L has been masked byreflecting means 150. The reflecting means 150 is in a stripe extendingover the whole active length of the probe. The purposes of thereflecting stripe is to return the laser energy back into the section,and thus restrict the emission of laser energy to a portion of thetissue that is adjacent to the cylindrical wall of the tube. Such probesmay be useful in lumens where only a limited sector of the lumenrequires irradiation. The buffer of the fiber-optic can be given astripe that is coaxial with the reflecting stripe and thus enable thesurgeon to orient the probe correctly. The stripe 150 consists of areflective coating applied to the outside of the tube 122. Such coatingsare available from numerous suppliers. One such supplier is SpectrumThin Films (Bohemia, N.Y.). If necessary, a plastic sleeve (not shown)may be applied, as for example by heat-shrinking, to protect thecoating. Alternately, the reflective stripe may be applied to aninternal surface of the probe.

[0076] Referring now to FIG. 3, the third embodiment of the inventioncomprises a probe 210 in combination with a catheter indicated generallyby the reference numeral 260 providing liquid cooling of the probe tip.The probe 210 shown in FIG. 3 is generally similar to the firstembodiment shown in FIG. 1, and features embodied in FIG. 3 that arecommon with features in FIG. 1 share like numbers, increased by 200.Thus, the probe 210 is attached to an optical fiber 212 having a core214 surrounded by cladding 216, encased within a buffer 220. A tube 222,an end cap 234, and so on, may be substantially the same as thosedescribed above with reference to FIG. 1. In this embodiment, however,the reflecting means 236 is a metallic mirror surface applied on theplug 234, and a partially reflecting means 262 has been applied to theproximal face of each of the bulkheads 226 a and 226 b that separate thesections 224 a, 224 b, and 224 c. A similar reflective coating may alsobe applied to the distal faces of the bulkheads 226, or a coating may beapplied to only the distal face of a bulkhead.

[0077] The catheter 260 has an inner working channel 263, in which thefiber-optic cable 212 and the probe 210 have been inserted, and an outerworking channel 264. The channels 263 and 264 are separated by a tube266. The distal end of the tube 266 is just short of the distal end ofthe optical fiber 212. The outer wall of the catheter 260 is formed by aplastic sheath 268 that is transparent to the treatment laserwavelength, which is closed at its distal end and encloses the probe210. The sheath 268 thus defines a plenum 270, which surrounds theactive length L of the probe 210 and is open to both of the workingchannels 263 and 264. Fluid coolant, which may be, for example, sterilewater can be delivered to the plenum 270 through the outer workingchannel 264, allowed to swirl freely within the plenum, and withdrawnthrough the inner working channel 263, as shown by the arrows F in FIG.3.

[0078] The coolant serves two purposes. First, it prevents the tissueadjacent the sheath 268 and proximate to the active length L fromoverheating. If the tissue should overheat, it may char or otherwiseimpede the penetration of the laser energy into the tissue to becoagulated. Second, the coolant prevents the active length L, includingthe reflecting means 236 and 262 and the plug 234, from overheating. Thecoolant carries off such heat as it is conducted from the surgical sitevia the inner working channel 263. The coolant has no direct contactwith the tissue being treated.

[0079] A suitable catheter, called Irrigated Power Laser Applicator Kit,is available commercially from Somatex® Medizintechnische Instrumente(Rietzneuendorf/b. Berlin, Germany).

[0080] The present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification, as indicating the scope of theinvention.

[0081] For example, although the probe 10 shown in FIG. 1 and the probe210 shown in FIG. 3 have three light-emitting sections 24 and the probe110 shown in FIG. 2 has two light-emitting sections, any of those probesmay have a different number of sections, depending on the requirementsof a particular application. It will be appreciated by those skilled inthe art that a greater number of sections can allow a more precisecontrol over the distribution of emitted light along the length of theprobe, but that a smaller number of sections allows simpler manufactureand a more economical product.

What is claimed is:
 1. A light-emitting probe comprising: a flexible, light-transmissive housing having a proximal end, adapted to be mounted to and to receive light from a fiber-optic, and a closed distal end; at least one optical spacer dividing the length of the interior of the housing into at least two sections such that the most proximal section abuts the fiber-optic; and a light-transmissive and light-dispersing medium filling each section.
 2. A probe according to claim 1, wherein the index of refraction of the at least one spacer is greater than the index of refraction of the light-transmissive and light-dispersing medium.
 3. A probe according to claim 1, wherein the light-transmissive and light-dispersing medium comprises a light-dispersing material in a light-transmissive matrix.
 4. A probe according to claim 1, wherein said light dispersing medium in different said sections has different dispersing powers.
 5. A probe according to claim 1, wherein said light dispersing medium in different said sections comprises different concentrations of a light-dispersing material in a light-transmissive matrix.
 6. A probe according to claim 1, further comprising a reflector at the distal end of the most distal said section.
 7. A probe according to claim 6, wherein the reflector comprises a metal layer.
 8. A probe according to claim 6, wherein the reflector comprises a mirror of thin layers of dielectric film.
 9. A probe according to claim 6, wherein the reflector comprises a birefringent material.
 10. A probe according to claim 6, wherein the reflector comprises layers designed to reflect the light back into the housing and exhibits multiple indexes of refraction at each layer.
 11. A probe according to claim 1, wherein the housing is transparent.
 12. A probe according to claim 11, wherein the housing comprises a transparent tube sealed off by a plug at the distal end.
 13. A probe according to claim 12, further comprising a reflector formed on the end plug.
 14. A probe according to claim 1, wherein the light-transmissive housing is a housing that is substantially non-absorptive of light passing through it.
 15. A probe according to claim 14, wherein the housing is light-transmissive for infra-red light with a wavelength in the range from 940 to 1064 nm.
 16. A probe according to claim 1, further comprising a partially-reflecting layer on at least one end face of said at least one optical spacer.
 17. A probe according to claim 1, further comprising a fiber-optic adapted to conduct light from a source and to which the proximal end of the housing is mounted.
 18. A probe according to claim 14, further comprising a sheath surrounding said probe and arranged in use to be supplied with a coolant liquid.
 19. A probe according to claim 15, further comprising a catheter surrounding the fiber-optic and defining channels to supply and remove said coolant liquid.
 20. A light-emitting probe comprising: a flexible, light-transmissive housing, having a proximal end adapted to be connected to a source of laser light and a distal end; within said housing a light-transmissive and light-dispersing medium, divided along the length of said housing into at least two sections having distinct light-dispersing properties; and a reflecting means at the distal end of said housing arranged to reflect the light back into the light-dispersing medium.
 21. A probe according to claim 20, wherein the light-transmissive and light-dispersing medium comprises a light-dispersing material in a light-transmissive matrix.
 22. A probe according to claim 21, wherein said light-dispersing medium in different said sections comprises different concentrations of said light-dispersing material in said light-transmissive matrix.
 23. A probe according to claim 20, wherein the reflector comprises a metal layer.
 24. A probe according to claim 20, wherein the reflector comprises a mirror of thin reflecting film layers.
 25. A probe according to claim 20, wherein the reflector comprises a birefringent material.
 26. A probe according to claim 20, wherein the reflector comprises layers designed to reflect the light back into the housing and exhibits multiple indexes of refraction at each layer.
 27. A probe according to claim 20, wherein the housing is transparent.
 28. A probe according to claim 27, wherein the housing comprises a transparent tube sealed off by a plug at the distal end.
 29. A probe according to claim 28, wherein the reflector is formed on the end plug.
 30. A probe according to claim 20, wherein the light-transmissive housing is a housing that is substantially non-absorptive of light passing through it.
 31. A probe according to claim 30, wherein the housing is light-transmissive for infra-red light with a wavelength in the range from 940 to 1064 nm.
 32. A probe according to claim 20, further comprising a fiber-optic adapted to conduct light from a source and to which the proximal end of the housing is mounted.
 33. A probe according to claim 32, further comprising a sheath surrounding said probe and arranged in use to be supplied with a coolant liquid.
 34. A probe according to claim 33, further comprising a catheter surrounding the fiber-optic and defining channels to supply and remove said coolant liquid.
 35. A probe according to claim 20, further comprising at least one optical spacer separating said at least two sections.
 36. A probe according to claim 35, further comprising a partially-reflecting layer on at least one end face of said at least one optical spacer.
 37. A probe according to claim 35, wherein the index of refraction of the at least one spacer is greater than the index of refraction of the light-transmissive and light-dispersing medium.
 38. A light-emitting probe comprising: a flexible, light-transmissive housing, having a proximal end adapted to be connected to a source of laser light and a distal end; a light-transmissive and light-dispersing medium within said housing; and a reflector at the distal end of said housing arranged to reflect the light back into the light-dispersing medium, wherein the reflector comprises layers designed to reflect the light back into the housing and exhibits multiple indexes of refraction at each layer.
 39. A probe according to claim 38, wherein the light-transmissive and light-dispersing medium comprises a light-dispersing material in a light-transmissive matrix.
 40. A probe according to claim 38, wherein the light-transmissive and light-dispersing medium is divided along the length of said housing into at least two sections having distinct light-dispersing properties.
 41. A probe according to claim 40, wherein said light dispersing medium in different said sections comprises different concentrations of a light-dispersing material in a light-transmissive matrix.
 42. A probe according to claim 40, further comprising at least one optical spacer separating said at least two sections.
 43. A probe according to claim 42, wherein the index of refraction of the at least one optical spacer is greater than the index of refraction of the light-transmissive and light-dispersing medium.
 44. A probe according to claim 42, further comprising a partially-reflecting layer on at least one end face of said at least one optical spacer.
 45. A probe according to claim 38, wherein the reflector comprises metal layers.
 46. A probe according to claim 38, wherein the reflector comprises a mirror of thin reflecting film layers.
 47. A probe according to claim 38, wherein the reflector comprises a birefringent material.
 48. A probe according to claim 38, wherein the housing comprises a transparent tube sealed off by a plug at the distal end.
 49. A probe according to claim 48, wherein the reflector is formed on the end plug.
 50. A probe according to claim 38, wherein the light-transmissive housing is a housing that is substantially non-absorptive of light passing through it.
 51. A probe according to claim 50, wherein the housing is light-transmissive for infra-red light with a wavelength in the range from 940 to 1064 nm.
 52. A probe according to claim 38, further comprising a fiber-optic adapted to conduct light from a source and to which the proximal end of the housing is mounted.
 53. A probe according to claim 52, further comprising a sheath surrounding said probe and arranged in use to be supplied with a coolant liquid.
 54. A probe according to claim 53, further comprising a catheter surrounding the fiber-optic and defining channels to supply and remove said coolant liquid.
 55. A method of making a light-emitting probe comprising a flexible, light-transmissive housing having a proximal end, adapted to be mounted to and to receive light from a fiber-optic, and a closed distal end, and a light-transmissive and light-dispersing medium within said housing; said method comprising preparing said medium by a method comprising the steps of: mixing under partial vacuum a fluid matrix and a dispersant, whereby included air within the medium is induced to froth at the surface; suddenly breaking the vacuum, thereby bursting air bubbles forming the froth; and repeating said steps until said medium is free from streaks and swirls and no further froth forms.
 56. A method of manufacturing a light-emitting probe, comprising the steps of: mounting a proximal end of a flexible, light-transmissive housing to a fiber-optic to receive light therefrom; introducing a hardenable fluid light-transmissive and light-dispersing medium into a first section of said housing abutting the fiber optic; as said medium is introduced, inspecting for trails of latent air; forming at least one puncture through said housing with a sharp needle at the most proximal point of at least one prominent air trail; inserting an end-cap to close the distal end of said housing, and urging said end cap as a piston to compress said medium and express air through said at least one puncture; and causing or permitting said medium to harden and seal said at least one puncture.
 57. A method according to claim 56, further comprising the steps of: inserting an optical spacer distally of said light-transmissive and light-dispersing medium dividing the length of the interior of the housing into two sections; introducing a light-transmissive and light-dispersing medium into a second section of said housing abutting said spacer distally thereof; and optionally inserting at least one further spacer to define at least one further section, and introducing a light-transmissive and light-dispersing medium into said at least one further section. 